How severe is CVE-2021-21002?

CVE-2021-21002 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-21002 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21002?

CVE-2021-21002 primarily affects Phoenixcontact Fl Comserver Uni 232/422/485 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-21002?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-21002 published?

CVE-2021-21002 was published on 2021-06-25 and last updated on 2026-06-17.

CVE-2021-21002

CVE-2021-21002 is a high-severity vulnerability in Phoenixcontact Fl Comserver Uni 232/422/485 Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-772.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (57th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-772
Affected product: Phoenixcontact Fl Comserver Uni 232/422/485 Firmware
Published: 2021-06-25
Last modified: 2026-06-17

Description

In Phoenix Contact FL COMSERVER UNI in versions < 2.40 a invalid Modbus exception response can lead to a temporary denial of service.

Frequently asked questions

What is CVE-2021-21002?: In Phoenix Contact FL COMSERVER UNI in versions < 2.40 a invalid Modbus exception response can lead to a temporary denial of service.
How severe is CVE-2021-21002?: CVE-2021-21002 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-21002 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21002?: CVE-2021-21002 primarily affects Phoenixcontact Fl Comserver Uni 232/422/485 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-21002?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-21002 published?: CVE-2021-21002 was published on 2021-06-25 and last updated on 2026-06-17.

References

https://cert.vde.com/en-us/advisories/vde-2021-022

Affected products (2)

cpe:2.3:o:phoenixcontact:fl_comserver_uni_232\/422\/485_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:phoenixcontact:fl_comserver_uni_232\/422\/485-t_firmware:*:*:*:*:*:*:*:*

Other CWE-772 vulnerabilities

CVE-2020-12134 — Critical (CVSS 9.8): Nanometrics Centaur through 4.3.23 and TitanSMA through 4.2.20 mishandle access control for the syslog log.
CVE-2017-15032 — Critical (CVSS 9.8): ImageMagick version 7.0.7-2 contains a memory leak in ReadYCBCRImage in coders/ycbcr.c.
CVE-2017-14138 — Critical (CVSS 9.8): ImageMagick 7.0.6-5 has a memory leak vulnerability in ReadWEBPImage in coders/webp.c because memory is not freed in…
CVE-2017-11641 — Critical (CVSS 9.8): GraphicsMagick 1.3.26 has a Memory Leak in the PersistCache function in magick/pixel_cache.c during writing of Magick…
CVE-2020-14339 — High (CVSS 8.8): A flaw was found in libvirt, where it leaked a file descriptor for `/dev/mapper/control` into the QEMU process. This…
CVE-2018-19760 — High (CVSS 8.8): cfg_init in confuse.c in libConfuse 3.2.2 has a memory leak.

Browse all CWE-772 vulnerabilities →